NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Peter Fogg
Date: 2005 Feb 25, 09:55 +1100
Yesterday I wrote, in
response to Jared’s
"I'm still not certain
that you can focus a picture after it has been taken, and get THE SAME result
as having focused it before."
No. Increasing edge contrast
won't affect focus. An image perfectly focused can be defined as having all its
rays of light coinciding at the same plane.
Since then I’ve
thought of another way of putting it. An image perfectly focused has each point
of light from the object resolved as a point. An image imperfectly focused
shows each point as a circle, and the more out of focus it is the bigger the
circle. All of these circles overlap, giving the familiar fuzzy out of focus
look. As far as I know there is no way to separate and then reduce the diameter
of each overlapping circle, which is what would be needed to improve the focus,
from a frozen image (still or movie).
'Sharpness' is in
parenthesis because it is subjective, whereas its components of resolution and
contrast are objective.
